The present invention relates generally to sewer cleaning machines wherein cleaning is performed by a high pressure hose terminated by a jet nozzle which pulls the hose through the sewer by rearwardly directed water jets and, more particularly, to a method and apparatus for use in such machines for generating high pressure pulses at the water jets to assist cleaning by pulsating or hammering penetration of blockages formed by concentrated accumulations of refuse and debris.
High pressure water flushing is a recognized effective way of cleaning both storm and sanitary sewers. In such sewer cleaning systems, a length of hose is unwound from a reel carried on a truck with the hose being inserted into a sewer to be cleaned. The end of the hose carries a jet nozzle which pulls itself and the hose through the sewer by the force of its rearwardly directed high pressure water jets which, at the same time, wash debris in the sewer back toward the cleaning entryway. The reel is rotated by a motor which is controlled by an operator of the cleaning system such that the hose is fed out at a rate consistent with its progress through the sewer. After the nozzle has traveled for a distance through the sewer, the motor connected to the reel is reversed to rewind the hose into the reel. This process is repeated several times until the length of sewer is clean.
As the nozzle pulls and advances the hose through the sewer, the nozzle may encounter a blockage caused by the collection of a substantial amount of refuse and debris which blockage momentarily hinders the advancement of the hose. It has been recognized that pulsation of the high pressure water within the hose creates a pulsating or hammering action at the nozzle to assist in the penetration of blockages within sewers. One approach to obtaining hammering action is to use a single piston high pressure pump as opposed to a three piston pump. A single piston pump inherently and continuously generates high amplitude pulsations at a frequency of approximately 1 hertz as opposed to a three piston pump which provides a substantially constant high pressure to the hose. Unfortunately, the continuous hammering action created by a single piston pump can lead to premature failure of the sewer cleaning system.
Another approach to obtaining pulsating or hammering action is to provide a hand operated valve on the pressure side of a high pressure pump used to operate a sewer cleaning system. This valve bleeds the cleaning fluid back to the holding tank or other source for the fluid. By manually throwing a lever which controls the valve, a single pulse is introduced at the hose nozzle because of the opening and closing of the valve such that high pressure pulses can be manually introduced by the machine operator. While this approach prevents the continuous hammering action which can lead to early deterioration of the cleaning system, to be effective it requires concentration on the part of the operator to determine when a blockage has been encountered by the nozzle and then the repeated operation of the control lever for the bleeder valve until the blockage has been penetrated.
Accordingly, there is a need for a method and apparatus for selectively generating a pulsating or hammering action at the nozzle of a high pressure sewer cleaning hose which is not demanding on an operator of the system and, preferably, is automatically activated upon the nozzle encountering a blockage in a sewer such that it not only relieves the cleaning system operator of tedious duties but also is not dependent for its activation upon the attentive observations of the operator.